A liquid chromatography/mass spectrometer (LC/MS) has been widely used in analysis of a biological sample, etc. In an ion source of LC/MS, gaseous ions are generated from a sample liquid separated by LC and introduced into a mass spectrometer section. As an ionization method in the ion source, a spray ionization method employing an electrospray ionization method (ESI) has been widely used. Between LC and the ion source of the mass spectrometer, generally a capillary which is a tube having an inner diameter of about several micrometers to several hundreds of micrometers is used. This electrospray ionization is performed at an atmospheric pressure, and a high voltage is applied between a sample liquid in an end portion of the capillary arranged in LC and a counter electrode (an inlet of the mass spectrometer section), and charged liquid droplets are generated by an electro-static spray phenomenon. The generated charged liquid droplets are evaporated to form gaseous ions. As the size of the charged liquid droplets generated first is smaller and the charge amount thereof is larger, the generation efficiency of gaseous ions is increased.
In recent electrospray ionization, nanoelectrospray in which the inner diameter of a capillary to be used for introducing a sample is decreased from about 100 μm to about 1 to 2 μm has come to be performed. By this nanoelectrospray, it has become possible to perform measurement of a sample or the like with an extremely small volume for a long time, and therefore to realize analysis of a biomolecule with an extremely small amount.
PTL 1, PTL 2, and NPL 1 disclose an ionization method using a probe. PTL 1 describes an ionization method in which a movable assistant probe is placed in a flow channel in a tube through which a sample in a capillary flows, and by oscillating and moving the assistant probe, the sample is supplied to a sampling probe disposed at an opposite position. PTL 2 and NPL 1 describe an ionization method in which adhesion of a sample (sampling) and ionization are performed by oscillating a probe up and down between an original point and the sample.